Lysergic acid diethylamide (LSD),also known colloquially as acid, is a hallucinogenic drug. Effects typically include altered thoughts, feelings, and awareness of one’s surroundings. Many users have visual or auditory hallucinations. Dilated pupils, increased blood pressure, and increased body temperature are typical. Effects typically begin within half an hour and can last for up to 12 hours. It is used mainly as a recreational drug or for spiritual reasons. LSD does not appear to be addictive, although tolerance may occur with use of increasing doses. Adverse psychiatric reactions are possible, such as anxiety, paranoia, and delusions. Distressing flashbacks might occur in spite of no further use, a condition called hallucinogen persisting perception disorder. Death as a result of LSD overdose is virtually unknown; on extremely rare occasions, however, death can be the result of accidents or reckless behavior. The effects of LSD are believed to occur as a result of alterations in the serotonin system. As little as 20 micrograms can produce a noticeable effect. In pure form, LSD is clear or white in color, has no smell, and is crystalline. It breaks down with exposure to ultraviolet light. As of 2017, about 10 percent of people in the United States have used LSD at some point in their lives, while 0.7 percent have used it in the last year. It was most popular in the 1960s to 1980s.The use of LSD among US adults increased 56.4% from 2015 to 2018.LSD is typically either swallowed or held under the tongue. It is most often sold on blotter paper and less commonly as tablets or in gelatin squares. LSD was first made by Albert Hofmann in 1938 from lysergic acid, a chemical from the fungus ergot. Hofmann discovered its hallucinogenic properties in 1943.In the 1950s, the Central Intelligence Agency (CIA) believed that the drug might be useful for mind control, so they tested it on people, some without their knowledge, in a program called MKUltra. LSD was sold as a medication for research purposes under the trade-name Delysid in the 1950s and 1960s. It was listed as a schedule 1 controlled substance by the United Nations in 1971.It currently has no approved medical use. In Europe, as of 2011, the typical cost of a dose was between €4.50 and €25.In November 2020, a referendum determined that it would be decriminalized in the US state of Oregon